The invention relates to a noise suppressor with a bypass resonator.
Connecting a bypass resonator to a noise suppressor in the air intake duct of an internal combustion engine is already disclosed in AT Patent 216,292. Such a bypass resonator leads to an improvement of the noise suppressor, especially near its natural resonance frequency, this frequency being determined by the dimensions and geometric configuration of the bypass resonator, also known as a Helmholtz resonator in shunt. To make it possible to adapt to different sound conditions, complex mechanical devices or a separate resonator for every sound condition are often necessary.
It is the object of the invention to provide a noise suppressor of the kind referred to above such that the (noise) damping characteristics can be influenced in a simple manner.
The noise suppressor according to the invention is advantageously able, to achieve the stated object as described and claimed hereinafter. Because the tubular connections between the sound-carrying duct and the bypass resonator are exchangeable parts which extend with various respective lengths into the bypass resonator, different natural resonances of the system can be adjusted in a simple manner.
In a second advantageous working embodiment of the invention, at least two tubular connections each having a different diameter are present, which are respectively connected with the bypass resonator through an alternately closing and opening flap valves; in an additional position, both can also be open or both can be closed. This control flap is mechanically simple to make, and its switching operationxe2x80x94in the case of a rotating control flap, for example, which depending on its rotational position respectively closes one opening and opens the otherxe2x80x94can be accomplished by an electric motor or also by a pressure chamber.
In a third working embodiment, the tubular connection is connected to a bypass resonator of a type whose volume which can be coupled to the tubular connection can be increased or decreased by means of a control flap. For example, the tubular connection can be coupled to the cylindrical outer surface of a hollow cylindrical bypass resonator, and the volume in the interior of the bypass resonator can be defined on one side by a stationary wall from the central axis to the outside wall and on the other side by movable wall which is continuously displaceable around the central axis or which can locked in various position settings.
Advantageously, the adjustment of the above-described pivotable flap or the wall can be effected by means of an electric motor or a pressure chamber. In the case of adjustment by means of the pressure chamber a push rod operated by the pressure chamber, which can be stopped in prescribed positions, can be provided. The latching of the push rod in the stops or switching positions can be achieved for example by a ball which catches under the pressure of a spring in recesses in the push rod. Without this push rod according to the embodiment, a pressure chamber operation, for example through a magnetic control valve, would catch only in the front and in the rear position when the vacuum is applied or is not applied.
In the case of a preferred application, the sound carrying duct is the intake duct for the intake air of an internal combustion engine and the noise emissions to be suppressed are generated by the air intake pulses of the individual cylinders. In the above-described embodiment with a pressure chamber and a push rod, one adjustment position for the adjustment of the resonator can be set in a state in which the intake duct vacuum is greatest in the low rotational speed range of the internal combustion engine and thus the vacuum box spring is compressed. A second adjustment position can be set in the case of weaker intake duct vacuum in the middle rotational speed range, and a third adjustment position can be set in the case of very weak intake duct vacuum in the higher rotational speed range and stronger spring force of the pressure chamber toward the push rod.
These and additional features of preferred embodiments of the invention will be found not only in the claims but also in the description and the drawings, whereby the individual features can be realized individually or jointly in the form of subcombinations in embodiments of the invention and in other fields and may represent advantageous as well as independently patentable embodiments, for which protection is hereby claimed.